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Full-Text Articles in Physics
Accelerated Taylor Plumes For Mif Targets, Michael R. Brown, D. A. Schaffner, Holden L. Parks , '16, Ariel B. Rock , '16
Accelerated Taylor Plumes For Mif Targets, Michael R. Brown, D. A. Schaffner, Holden L. Parks , '16, Ariel B. Rock , '16
Physics & Astronomy Faculty Works
The SSX plasma device has been converted to a 2.5 m merging plasma wind tunnel configuration. Experiments are underway to study merging and stagnation of high density, helical Taylor states\footnote{Gray, et al, PRL {\bf 110}, 085002 (2013).} to employ as a potential target for magneto-inertial fusion. Eventually, SSX Taylor states will be accelerated to over 100 km/s and compressed to small volumes either by stagnation or merging. Initial un-accelerated merging studies produce peak proton densities of 5×1015 cm−3. Densities are measured with a precision quadrature He-Ne laser interferometer. Typical merged plasma parameters are Ti=20 eV,Te=10 eV,B=0.4 T with lifetimes of …
Multifractal And Monofractal Scaling In A Laboratory Magnetohydrodynamic Turbulence Experiment, D. A. Schaffner, Michael R. Brown
Multifractal And Monofractal Scaling In A Laboratory Magnetohydrodynamic Turbulence Experiment, D. A. Schaffner, Michael R. Brown
Physics & Astronomy Faculty Works
Both multifractal and monofractal scaling of structure function exponents are observed in the turbulent magnetic fluctuations of the Swarthmore Spheromak Experiment plasma. Structure function and probability distribution function (PDF) analysis exhibits multifractal scaling exponents in low frequency, inertial range fluctuations of the turbulence but monofractal scaling in higher frequency, dissipation range fluctuations. The transition from multifractal to monofractal scaling occurs rapidly suggesting a dissipation mechanism that is insensitive to turbulent structure scale size. Structure functions and PDFs are presented for both temporal and spatial measurements. Variations in the magnetic helicity in the plasma are also shown to modify multifractal scaling …
Liquid Crystal Janus Emulsion Droplets: Preparation, Tumbling, And Swimming, J. Jeong, A. Gross, W.-S. Wei, F. Tu, D. Lee, Peter J. Collings, A. G. Yodh
Liquid Crystal Janus Emulsion Droplets: Preparation, Tumbling, And Swimming, J. Jeong, A. Gross, W.-S. Wei, F. Tu, D. Lee, Peter J. Collings, A. G. Yodh
Physics & Astronomy Faculty Works
This study introduces liquid crystal (LC) Janus droplets. We describe a process for the preparation of these droplets, which consist of nematic LC and polymer compartments. The process employs solvent-induced phase separation in emulsion droplets generated by microfluidics. The droplet morphology was systematically investigated and demonstrated to be sensitive to the surfactant concentration in the background phase, the compartment volume ratio, and the possible coalescence of multiple Janus droplets. Interestingly, the combination of a polymer and an anisotropic LC introduces new functionalities into Janus droplets, and these properties lead to unusual dynamical behaviors. The different densities and solubilities of the …
Ssx Mhd Plasma Wind Tunnel, Michael R. Brown, D. A. Schaffner
Ssx Mhd Plasma Wind Tunnel, Michael R. Brown, D. A. Schaffner
Physics & Astronomy Faculty Works
A new turbulent plasma source at the Swarthmore Spheromak Experiment (SSX) facility is described. The MHD wind tunnel configuration employs a magnetized plasma gun to inject high-beta plasma into a large, well-instrumented, vacuum drift region. This provides unique laboratory conditions approaching that in the solar wind: there is no applied background magnetic field in the drift region and has no net axial magnetic flux; the plasma flow speed is on the order of the local sound speed (M ~ 1), so flow energy density is comparable to thermal energy density; and the ratio of thermal to magnetic pressure is of …
Chiral Structures And Defects Of Lyotropic Chromonic Liquid Crystals Induced By Saddle-Splay Elasticity, Z. S. Davidson, L. Kang, J. Jeong, T. Still, Peter J. Collings, T. C. Lubensky, A. G. Yodh
Chiral Structures And Defects Of Lyotropic Chromonic Liquid Crystals Induced By Saddle-Splay Elasticity, Z. S. Davidson, L. Kang, J. Jeong, T. Still, Peter J. Collings, T. C. Lubensky, A. G. Yodh
Physics & Astronomy Faculty Works
An experimental and theoretical study of lyotropic chromonic liquid crystals (LCLCs) confined in cylinders with degenerate planar boundary conditions elucidates LCLC director configurations. When the Frank saddle-splay modulus is more than twice the twist modulus, the ground state adopts an inhomogeneous escaped-twisted configuration. Analysis of the configuration yields a large saddle-splay modulus, which violates Ericksen inequalities but not thermodynamic stability. Lastly, we observe point defects between opposite-handed domains, and we explain a preference for point defects over domain walls.
Magnetohydrodynamic Turbulence: Observation And Experiment, Michael R. Brown, D. A. Schaffner, Peter J. Weck , '15
Magnetohydrodynamic Turbulence: Observation And Experiment, Michael R. Brown, D. A. Schaffner, Peter J. Weck , '15
Physics & Astronomy Faculty Works
We provide a tutorial on the paradigms and tools of magnetohydrodynamic(MHD)turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuationsEB(f). We will describe five useful statistical tools for MHDturbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHDfluctuations in the solar wind. A single dataset from the Wind satellite will be …
Self-Organized Assemblies Of Colloidal Particles Obtained From An Aligned Chromonic Liquid Crystal Dispersion, N. Zimmermann, G. Jünnemann-Held, Peter J. Collings, H.-S. Kitzerow
Self-Organized Assemblies Of Colloidal Particles Obtained From An Aligned Chromonic Liquid Crystal Dispersion, N. Zimmermann, G. Jünnemann-Held, Peter J. Collings, H.-S. Kitzerow
Physics & Astronomy Faculty Works
The behavior of mono-disperse colloidal particles in a chromonic liquid crystal was investigated. Poly(methyl methacrylate) spherical particles with three different functionalizations, with and without surface charges, were utilized in the nematic and columnar phases of disodium cromoglycate solutions. The nematic phase was completely aligned parallel to the glass substrates by a simple rubbing technique, and the columnar phase showed regions of similar alignment. The behavior of the colloidal particles in the chromonic liquid crystal depended critically on the functionality, with bromine functionalized particles not dispersing at all, and cationic trimethylammonium and epoxy functionalized particles dispersing well in the isotropic phase …
Permutation Entropy And Statistical Complexity Analysis Of Turbulence In Laboratory Plasmas And The Solar Wind, Peter J. Weck , '15, D. A. Schaffner, Michael R. Brown, R. T. Wicks
Permutation Entropy And Statistical Complexity Analysis Of Turbulence In Laboratory Plasmas And The Solar Wind, Peter J. Weck , '15, D. A. Schaffner, Michael R. Brown, R. T. Wicks
Physics & Astronomy Faculty Works
The Bandt-Pompe permutation entropy and the Jensen-Shannon statistical complexity are used to analyze fluctuating time series of three different turbulent plasmas: the magnetohydrodynamic (MHD) turbulence in the plasma wind tunnel of the Swarthmore Spheromak Experiment (SSX), drift-wave turbulence of ion saturation current fluctuations in the edge of the Large Plasma Device (LAPD), and fully developed turbulent magnetic fluctuations of the solar wind taken from the Wind spacecraft. The entropy and complexity values are presented as coordinates on the CH plane for comparison among the different plasma environments and other fluctuation models. The solar wind is found to have the highest …